High-Resolution UHV Electron Microscopy of Reconstructed and Adsorbed Surfaces

Abstract

High-resolution electron microscopy (HREM) has been applied for structure analyses of reconstructed and adsorbed surfaces at atomic resolution in transmission (TEM) and reflection (REM) mode by using an UHV electron microscope (modified 2000 FXV). In the last ICEM conference, we reported instrumental design of the new UHV electron microscopet[1] with a review on atomic structure study by UHV -EM[2]. In this review we show dynamic structural studies of surfaces which have been revealed by using a TV camera-and-video recording system. Details of each topic shown here are given in original papers[3-8].The UHV electron microscope of 200 keV has the theoretical point-to-point resolution of 0.21 nm. The microscope has two exchange system for evaporators and a gas-inlet system. Surface structural changes recorded on a video tape are resolved at time resolution of 1/30 sec. Figures shown are reproduced from the video frames.High-Resolution REMIn REM mode, we obtain lattice fringes of the surface superlattices by interference of reflections so that the position of the fringes vary with the excitation condition similarly to lattice fringes in TEM. In a certain reflection condition the lattice fringes can be regarded as the structure image. In case of Si(111)7×7 surface, positions of dark lattice fringes (0.23 nm spacing) of the 7×7 coincide almost with the steps[9,10].